Material control and test method of large vermicular graphite iron castings

In order to control the content of some trace elements (Ti, Pb, etc.) in Vermicular Graphite Cast Iron and ensure the processing performance, the main raw materials of vermicular graphite cast iron are the best. The specific standards are as follows:

(1) The best choice of high purity pig iron is low S, low P, low Ti and stable, high C, low Si pig iron;

(2) Low Ti carbon steel (such as Q235, q255, etc.) with regular shape, uniform thickness and stable type is recommended for vermicular iron scrap;

(3) The recycled material of vermicular graphite cast iron needs to be shot blasted;

(4) Graphitized and low S carburizing agent is selected;

8 T ABP medium frequency induction furnace, a domestic vermicular treatment station, OCC thermal analyzer, imported direct reading spectrometer and C-S analyzer were used to detect the composition of the original molten iron and the vermicular treated molten iron. The microstructure of the test block was observed by metallographic microscope, and the tensile strength and hardness of the test block were measured by tensile testing machine and hardness tester.

(a) Creep rate 80%

According to the different wall thickness of the casting, the size of the attached test block is designed, and the test results of its metallographic structure and mechanical properties meet the technical requirements. In order to ensure the casting performance, the metallographic examination of different positions shows that the creep rate of thick position (main bolt hole, camshaft hole) is 80%, and that of thin position is 85% (as shown in the figure).

(b) Creep rate 85%